The present invention relates to a transmission which is designed to transmit a mechanical power from a drive source to a rotating output member with a rotational speed change.
Gear type transmissions with combinations of gears have been used commonly as automobile transmissions. In general, such a gear type transmission comprises a plurality of gear trains with respective speed change ratios, each gear train constituting a corresponding power transmission path, and these power transmission paths are selected exclusively by actuating, for example, clutches which are arranged appropriately, for the speed ratio change of the transmission. As such a transmission, Japanese Laid-Open Patent Publication No. H11-13878 discloses a transmission used on an electric motorcar.
In such a transmission, the speed ratio change, which is executed by shifting or changing selectively the power transmission paths, takes a relatively short time, so the speed of the vehicle does not change much in such a short time, and the rotational speed of the output shaft of the transmission remains almost constant. However, when the speed change ratio of the transmission, i.e., the ratio of the rotational speeds of the output shaft and the input shaft, is changed or shifted, a corresponding change occurs in the rotational speed of the engine, which is coupled to the input shaft of the transmission. In this instance, the inertia of the engine experiencing the rotational speed change, exerts a torque to the output shaft, which may present a problem of xe2x80x9cshift shock.xe2x80x9d
It is an object of the present invention to provide a transmission which is designed to limit the above described effect of the changing rotational speed of the engine, which affects the rotation of the output shaft during shift operations.
The present invention provides a transmission which transmits a power from a drive source (for example, the electrical motor 1 described in the following embodiment) to an output rotating member (for example, the countershaft 30 described in the following embodiment) with a speed change. In this transmission, a drive side rotating member (for example, the main shaft 10 and the rotating members connected thereto) which is coupled to the drive source experiences a rotational change along with the drive source when a shift from a first speed ratio (for example, a LOW speed ratio) to a second speed ratio (for example, a SECOND speed ratio) is executed, and an intermediate rotating member (for example, the sun gear 13 and the rotating members connected thereto) which is positioned between the drive side rotating member and the output rotating member experiences a rotational change in a direction opposite to that of the drive side rotating member when the shift is executed. It is a feature of the present invention that the ratio of the rotational inertia of the drive side rotating member to the rotational inertia of the intermediate rotating member equals the reciprocal of the ratio of the rotational change of the drive source to the rotational change of the intermediate rotating member, these rotational changes being experienced during the shift.
When the transmission is shifted from the first speed ratio to the second speed ratio, the rotational speed of the drive source changes correspondingly to the speed change ratio of the shift between these two speed ratios. Because the ratio of the rotational inertia of the drive side rotating member to the rotational inertia of the intermediate rotating member is set equal to the reciprocal of the ratio of the rotational change of the drive source to the rotational change of the intermediate rotating member, which changes occur during the shift, the energy involved in the rotational change of the drive side rotating member equals the energy involved in the rotational change of the intermediate rotating member during the shift, with the directions of the rotational changes of the drive side rotating member and the intermediate rotating member being opposite to each other. As a result, these energies can offset each other, so the energies of these rotational changes are not transferred to the output rotating member of the transmission. Thus, the effect of shift shock is restrained to realize a smooth shift operation for the transmission.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.